1. Field of the Invention
This invention relates generally to a wellhead assembly for an oil and gas well. The invention may find use in a tubing hanger arrangement used in completion of an offshore oil and gas well and in completion of land oil and gas wells.
2. Description of the Prior Art
U.S. Pat. No. 7,604,047 which issued on Oct. 20, 2009 and U.S. Pat. No. 7,419,001 illustrate and describe a universal tubing hanger suspension assembly for an offshore well that includes a tubing hanger housing that is positioned in the wellhead housing independently of knowledge of details of a wellhead housing in which the tubing hanger is to be placed. As shown in FIG. 1, the prior tubing hanger suspension assembly 10 includes a tubing hanger housing 12 and a tubing hanger lower assembly 14. After the tubing housing 12 is installed in the wellhead 8 a Christmas tree connector 4 is run and connects to the housing 12, for mounting a Christmas tree on the wellhead 8.
Production tubing 22 is coupled to the bottom of the tubing hanger 12 by a threaded connection 20, with pin threads 5 cut in the tubing hanger housing 12 body coupled with box threads 6 of the production tubing 22. The tubing hanger housing 12 is supported in place by locking and sealing mechanism 34 between tubing hanger lower assembly 14 and production casing 18 below wellhead 8. The production casing hanger 18a is supported on the casing hanger 25. Both the tubing hanger housing 12 and the production tubing 22 must be made of Corrosion Resistant Alloy (CRA) material, because highly corrosive contaminants such as H2S in production fluid flowing in the production tubing 22 also contacts the interior of the tubing hanger housing 12. Accordingly, the large tubing hanger housing 12 as well as the production tubing 22 must be fabricated of expensive Corrosion Resistant Alloy.
It has been found that cutting the pin threads 5 of the large tubing hanger housing 12 of Corrosion Resistant Alloy material is extremely exacting, subject to error, resulting in a very high expense and risk of failure while fabricating the tubing hanger 12.